Field of the Invention
The invention relates to a material roll which includes a roll of a long sheet material including an optical film having first and second surfaces, a first base film provided on the first surface of the optical film with a first pressure-sensitive adhesive layer interposed therebetween, and a second base film provided on the second surface of the optical film with a second pressure-sensitive adhesive layer interposed therebetween and which is for use in a process comprising drawing the long sheet material from the roll, cutting at least the optical film into a predetermined length, and bonding the cut piece of the optical film to the surface of an optical display unit. The invention also relates to a system and a method for manufacturing an optical display device with the material roll.
Description of the Related Art
An example of the optical display device, which is incorporated in a liquid crystal display or the like, has a structure including an optical display unit and optical sheet pieces (including an optical film such as a polarizing film) bonded to one or both sides of the optical display unit. A known conventional method for manufacturing such an optical display device includes the steps of providing a roll of a long sheet material including an optical film and a release film (a first base film) bonded thereto, drawing the long sheet material from the roll, sequentially cutting the long sheet material in the transverse direction at intervals corresponding to the size of an optical display unit so that a cut piece of the sheet material is obtained, then peeling off the first base film from the cut piece of the sheet material to obtain an optical sheet piece having a first pressure-sensitive adhesive layer at the surface, and bonding the optical sheet piece to the optical display unit with the first pressure-sensitive adhesive layer interposed therebetween. Since the first base film is peeled off so that the optical sheet piece can be bonded to the optical display unit, the first base film is so formed that it can be relatively easily peeled off.
In the above conventional method of manufacturing an optical display unit, each manufactured piece of the sheet material is packaged by a film manufacturer and transported to a panel manufacturer, who unpacks each piece and bonds it to each optical display unit. The packaging is necessary, because the film manufacturer and the panel manufacturer are located at different places. However, the packaging is complicated and causes a problem in which the pieces of the sheet material may easily suffer from scratching or staining during transport or the like.
The technique disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2007-140046 uses a continuous manufacturing line in which the steps of cutting a long sheet material drawn from a material roll and bonding the cut piece of the sheet material to an optical display unit are performed. This can make the process simpler than the conventional method including packaging each piece of the sheet material and prevent scratching or staining during transport or the like.
Even in the technique disclosed in Japanese Patent Application Laid-Open (JP-A) No. 140046, the roll of the long sheet material has to be transported from a film manufacture to a panel manufacturer. Since only a little or stain can make defective an optical film such as a polarizing film in the long sheet material, a surface protecting film is bonded to the optical film so that the optical film can be protected from scratching or staining during transport or until the optical film is bonded to the optical display unit.
The surface protecting film corresponds to a second base film, which is peelably bonded to the surface of the optical film with a second pressure-sensitive adhesive layer interposed therebetween and will be peeled off together with the second pressure-sensitive adhesive layer after the optical sheet piece is bonded to the optical display unit. Since the second base film is peeled off from the optical film after the optical sheet piece is bonded to the optical display unit, the second pressure-sensitive adhesive layer is so formed that it can be relatively easily peeled off from the optical film.
As mentioned above, the first and second base films are so formed that they can be relatively easily peeled off. If the material roll is formed by winding a long sheet material in which such easily peelable base films are laminated, respectively, stress generated between each base film and the optical film may cause displacement between these films. In such a case, lifting may occur between each base film and the optical film, which may result in bubbles or wrinkles.
There is a problem in which if bubbles or wrinkles are formed between each base film and the optical film, the surface of the pressure-sensitive adhesive layer may be damaged, so that a defective product may be produced. In particular, there is a problem in which if such a material roll is placed in a high-temperature environment for a long time during transport or exposed to a shake, vibration, impact, or the like during transport, lifting may tend to occur between each base film and the optical film, so that the durability of the material roll may be reduced. If lifting occurs between each base film and the optical film, the thickness of the pressure-sensitive adhesive layer may be changed at the part where the lifting occurs, and the optical film wound in such a state may be deformed.
Such lifting can be a significant problem in a continuous process including drawing the long sheet material from the material roll and bonding the optical film to the optical display unit. Specifically, during the process from the step of drawing the long sheet material from the material roll to the step of bonding the optical film to the optical display unit, it is difficult to visually detect lifting generated in the long sheet material or treat the lifting as a defect. Even if defect inspection is automatically performed using a defect inspection apparatus, it will be difficult to reliably detect lifting with no false detection in the defect inspection apparatus. Thus, there is a problem in which an optical film deformed by lifting may be bonded to the optical display unit to form a defective optical display device.